Experiment: Converting AC to DC (Rectifiers)
Objectives:




To investigate the function of a diode
To convert AC into DC
To compare different types of rectifiers
To reduce DC-ripple
Material needed:
1 AC-Power supply (5V- 25V, depending on type of diode)
5 diodes (e.g. 1N4001, 1N4004)
1 electrolyte capacitor C1 (small capacity e.g. 22uF/40V)
1 electrolyte capacitor C2 (big capacity e.g. 1000uF/40V)
2 light bulbs (voltage depending on power supply voltage used)
1 bread board
1 oscilloscope (2 channels)
cables
Experiment 1: Half-Wave-Rectifier
1. Set up circuit 1
Cable 1
AC
UAC
UL
2. Use oscilloscope to display UAC (channel 1) and UL (channel2)
3. Bypass diode with cable 1
4. Adjust AC-Power Supply to the chosen voltage
5. Switch on AC-Power Supply
6. Graph UL for the protocol (UL=UL11)
7. Remove cable 1
8. Graph UL for the protocol (UL=UL12)
9. Add the smaller capacitor C1 to the circuit (parallel to the lamp)
10. Graph UL for the protocol (UL=UL1C1)
687302860/July2002/G.Vogt
CERN, HST2002, Small Experiment Group
1/5
11. Remove capacitor
12. Add the larger capacitor C2 to the circuit (parallel to the lamp)
13. Graph UL for the protocol (UL=UL1C2)
14. Switch off power supply
15. Disconnect oscilloscope
16. Analyze the resulted graphs
Experiment 2: Bridge-Rectifier (Full-Wave-Rectifier)
1. Set up circuit 2
A
C
UL
UAC
2. Use oscilloscope to display UL
ATTENTION !!! DO NOT MEASSURE UAC AND UL WITH THE
OSCILLOSCOPE SIMUNTANOUISLY !!!
Different ground potentials are connected. This can cause damage to the
oscilloscope or the electronic circuits.
3. Adjust AC-Power Supply to the chosen voltage
4. Switch on AC-Power Supply
5. Graph UL for the protocol (UL=UL21)
6. Add the smaller capacitor C1 to the circuit (parallel to the lamp)
7. Graph UL for the protocol (UL=UL2C1)
8. Remove capacitor
9. Add the larger capacitor C2 to the circuit (parallel to the lamp)
10. Graph UL for the protocol (UL=UL2C2)
11. Switch off AC-Power Supply
12. Analyze the resulted graphs
687302860/July2002/G.Vogt
CERN, HST2002, Small Experiment Group
2/5
Explanation:
Setup of the circuits for both types of
rectifiers: =>
The following diagrams show photos
taken from the screen of a digital
oscilloscope. Ground level is indicated by
the marks “1” and “2”.
HalfWave
Full-Wave
Experiment 1: Half-Wave-Rectifier:
UL11: UL11 = UAC, AC-50Hz Sine Wave, diode
bypassed
Voltage without capacitor (UL12):
UAC
UL12
Current in positive direction (anode =>
cathode, positive half-wave) can pass
the diode.
Current in negative direction (negative
half-wave) is not able to pass. => only
the positive half-wave appears.
Voltage with small capacitor C1 (UL1C1 ):
UAC
UL1C1
Capacitor C1 is charged by the
increasing voltage of the positive halfwave and discharged during the
decrease of the half-wave and the
zero-voltage period. Due to the small
capacitance voltage UL1C1 has high
ripple.
687302860/July2002/G.Vogt
CERN, HST2002, Small Experiment Group
3/5
Voltage with large capacitor C2 (UL1C2):
UAC
UL1C2
Due to the larger capacitance C2 the
voltage UL1C2 is not dropping so low
=> ripple is low.
Experiment 2: Bridge-Rectifier (Full-Wave-Rectifier):
ATTENTION !!! DO NOT MEASSURE UAC AND UL WITH THE OSCILLOSCOPE
SIMUNTANOUISLY !!! Here UAC is taken from a saved reference channel !!
Voltage without capacitor (UL21):
UAC
UL21
Positive and negative current can find
paths over the diode network. Therefore
the negative half-wave is clapped to
positive voltage.
Voltage with small capacitor C1 (UL2C1 ):
UAC
UL2C1
Capacitor C1 is charged by the increasing voltage and discharged during
the decreasing voltage. Because of the smaller decreasing period the
voltage UL2C1 does not drop so much.
687302860/July2002/G.Vogt
CERN, HST2002, Small Experiment Group
4/5
Voltage with large capacitor C2 (UL2C2):
UAC
UL2C2
Due to the larger capacitance C2 the voltage is not dropping so low
=> ripple is low.
Conclusion:
The two methods converting AC to DC are
shown =>
Top to bottom:
 Supplied AC-Voltage
 Half-Wave-Rectifier
 Bridge-rectifier
The ripple can be decreased by using
capacitors.
This experiment was designed and presented at
CERN, HST-2002 programme by:
Dipl.-Ing. Dr. Gerd Vogt
Hoehere Lehranstalt fuer Umwelt und Wirtschaft
3683 Yspertal, Austria
http://www.hlaysper.ac.at
gvogt@hlaysper.ac.at
687302860/July2002/G.Vogt
CERN, HST2002, Small Experiment Group
5/5